Method for heating a turbine shaft

ABSTRACT

A method for heating a turbine shaft is provided. The turbine shaft is heated by spraying warm water from a supply pump or from a pre-heating section. A steam turbine is also provided. The steam turbine includes a housing, wherein injection nozzles for injecting the water are arranged within the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2010/050800, filed Jan. 25, 2010 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 09001828.4 EP filed Feb. 10, 2009. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention refers to a method for heating a turbine shaft and also to a steam turbine comprising a turbine shaft and a device for heating the turbine shaft.

BACKGROUND OF INVENTION

In power plants, which are equipped with a steam turbine plant for power generation, it can be necessary, depending upon the current power requirement, to shut down an individual steam turbine or a plurality of steam turbines and, depending upon requirement, to restart them. A quick starting of the respective steam turbine plant is of vital importance in this case. This applies particularly to longer downtimes, especially after a cold start and after a hot start, for example after a weekend downtime. It is known during the starting process to first run up or heat up a steam generator in order to increase the steam temperature and the steam pressure. As soon as a prespecified starting temperature and a prespecified starting pressure and also a prespecified starting quality for the steam exist, a starting process for starting the steam turbine is initiated. For this purpose, inter alia, live steam valves are opened to a greater or lesser extent. In this case, the values for the starting temperature, for the starting pressure and for the starting quality of the steam are selected so that after starting the steam turbine a no-load operation or an on-load operation at low load can be realized for the steam turbine.

Up to initiation of the actual starting process, these parameters must be stable. Depending upon the power plant type and type of boiler construction or power plant size, about 1 to 3 hours can regularly elapse in this case. As a result of the admission of hot steam during starting from a cold machine state, high material loads as a result of the occurring thermal expansion stresses are regularly reached.

As a result of liberalization of the energy market, it is customary at present to take steam turbine plants out of operation over a longer time span. Associated with this are short-term downtimes or daily starting or stopping running methods and also weekend downtimes.

SUMMARY OF INVENTION

However, high flexibility is desired to be able to start the power plants quickly at any time. This is where the invention comes in, the object of which is to disclose a method and a steam turbine which can be heated up quickly.

This object is achieved by means of a method for heating a turbine shaft, wherein the turbine shaft is heated by means of water injection. The object which is directed towards the steam turbine is achieved by means of a steam turbine comprising a turbine shaft and a device for injecting water onto the turbine shaft.

The turbine shaft is customarily a large component with a high mass and consequently a comparatively high thermal capacity. This leads to the turbine shaft being heated comparatively slowly during an energy supply. An essential idea of the invention is to consequently heat the turbine shaft more quickly by hot water being injected onto the turbine shaft. As a result of this water injection, a quick transfer of heat of the hot water onto the turbine shaft is carried out. Water in its liquid physical state is understood by the term water in this case.

Advantageous developments are disclosed in the dependent claims. For an ideal transfer of heat of the hot water onto the turbine shaft, hot water or warmed water at temperatures between 100° C. and 350° C. is used. At the aforesaid temperatures of between 100° C. and 350° C., the water exists in a gaseous state.

In an advantageous development, the turbine shaft is heated by means of water injection before start-up. This leads to the turbine shaft already being heated in a very early stage as a result of the water injection. The steam turbine customarily has so-called casing drains which are naturally opened while the turbine shaft is sprayed upon with water. Providing the pressure in the steam turbine lies below the pressure of the injected water, the injected water is evaporated. During the subsequent condensation of the injected water on the cold components, the desired heating is consequently achieved. As a result, the turbine shaft is heated more quickly and can reach the operating temperature earlier in order to be connected to an electric supply network.

In an advantageous development, the turbine shaft is sprayed with water until a maximum warm-up speed is reached. The maximum warm-up speed in this case reaches values of between 8 Hz and 25 Hz. Since via the water injection a permanent transfer of heat onto the turbine shaft is realized, it is consequently advantageous that the water is constantly sprayed onto the turbine shaft until the turbine shaft has reached the maximum warm-up speed in the heating-up process. The start-up time is further curtailed as a result.

The hot water in this case is extracted from a feedwater heater string or from a feed pump in order to ensure the required steam purity, for example from a parallel steam source. In a steam turbine plant, a water steam cycle is usually provided in such a way that water is made available from the feedwater heater string or from the feed pump. The water from the feedwater heater string compared with the water from the pump is such that it has a higher temperature, the pressure in the turbine being of vital importance.

In an advantageous development, injection nozzles, via which the hot water is sprayed onto the turbine shaft, are arranged inside the steam turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained in more detail with reference to a drawing.

In the drawing:

FIG. 1 shows a schematic view of water injection onto a turbine shaft.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows in a schematic view a turbine shaft 1 with is of a double-flow design. This means the turbine shaft 1 comprises a left-hand flow 2 and a right-hand flow 3. The turbine shaft 1 rotates around the rotational axis 4. During operation, live steam flows into the steam turbine via an admission section, which is not shown in more detail, and expands along the left-hand flow 2 and the right-hand flow 3. Furthermore, the turbine shaft 1 comprises rotor blades, which are not shown in more detail. During operation, the turbine shaft 1 can be heated up to over 300° C. The temperatures can even reach values of up to 630° C. After a shutdown, the temperature of the turbine shaft 1 can be less than 100° C.

For quick heating of the turbine shaft 1, this is sprayed with hot water 5 from injection nozzles 6. The hot water 5 can have temperatures of between 100° C. and 350° C. During the heating up, the water in this case is directed via a valve 7 to the injection nozzle 6. With the valve 7, the amount of water which is directed through a line 8 to the injection nozzle 6 can be regulated.

The turbine shaft 1 in this case is heated by means of water injection before start-up. This means that the turbine shaft 1 is already sprayed with water during the turning operation, i.e. an externally supplied rotational movement via a motor. In so doing, however, care is to be thoroughly taken that the amount of water 5 which is sprayed from the injection nozzle 6 is distributed consistently over the surface of the turbine shaft 1 since otherwise local stresses can arise. Furthermore, the turbine shaft 1 is sprayed with hot water 5 by means of the injection nozzles 6 until a maximum warm-up speed is reached. The warm-up speed in this case attains values of between 8 Hz and 25 Hz.

The valve 7 is fluidically connected to a line 9, wherein the line 9, in a way not shown in more detail, is fluidically connected to a feedwater heater string or to a feed pump. This means that the hot water 5 is extracted from the feedwater heater string or from the feed pump. The choice of extraction depends upon the desired temperature of the hot water 5. Combinations are also conceivable, wherein the hot water 5 from the feedwater heater string or from the feed pump is mixed or else extracted from a parallel steam source, for example from a second power station unit.

The turbine shaft 1 is part of a steam turbine, which is not shown in more detail. This steam turbine comprises a casing, wherein the injection nozzles 6 for injecting the water 5 are arranged inside the casing. The position of the injection nozzles 6 and the flow volume of hot water 5 should be suitably selected so that the thermal transfer coefficient is optimum. Furthermore, the steam turbine has casing drains which are designed in such a way that water in the casing can drain off. These casing drains are opened during the heating process so that the water can drain off. 

1.-10. (canceled)
 11. A method for heating a turbine shaft, comprising: heating the turbine shaft by water injection by means of liquid water.
 12. The method as claimed in claim 11, wherein the turbine shaft rotates around a rotational axis during the water injection.
 13. The method as claimed in claim 12, wherein the water has temperature values of between 100° C. and 350° C.
 14. The method as claimed in claim 11, wherein the turbine shaft is heated by means of the water injection before start-up.
 15. The method as claimed in claim 11, wherein the turbine shaft is heated by means of the water injection until a maximum warm-up speed is reached.
 16. The method as claimed in claim 15, wherein the maximum warm-up speed attains values of between 8 Hz and 25 Hz.
 17. The method as claimed in claim 13, wherein the hot water is extracted from a feedwater heater string.
 18. The method as claimed in claims 13, wherein the hot water is extracted from a feed pump.
 19. A steam turbine, comprising: a turbine shaft having a turbine shaft surface; and a device for injecting liquid water onto the turbine shaft surface.
 20. The steam turbine as claimed in claim 19, further comprising a casing, wherein a plurality of injection nozzles for injecting the water are arranged inside the casing.
 21. The steam turbine as claimed in claim 19, wherein the turbine shaft rotates around a rotational axis during the water injection.
 22. The steam turbine as claimed in claim 21, wherein the water has temperature values of between 100° C. and 350° C.
 23. The steam turbine as claimed in claim 19, wherein the turbine shaft is heated by means of the water injection before start-up.
 24. The steam turbine as claimed in claim 19, wherein the turbine shaft is heated by means of the water injection until a maximum warm-up speed is reached.
 25. The steam turbine as claimed in claim 24, wherein the maximum warm-up speed attains values of between 8 Hz and 25 Hz.
 26. The steam turbine as claimed in claim 22, wherein the hot water is extracted from a feedwater heater string.
 27. The steam turbine as claimed in claims 22, wherein the hot water is extracted from a feed pump.
 28. A method for heating a turbine shaft, comprising: heating the turbine shaft by water injection by means of liquid water, wherein the water has temperature values of between 100° C. and 350° C., and wherein the hot water is extracted from a feed pump. 